MGB best Carb?

I just purchased my first MG, which is a 1977 MGB.
The car needs a rebuild because the car has been sitting for several years.
It has the original Zenith carb on it, and several people have told me to

replace it with a Weber carb as opposed to messing with the original because
the Zenith carb is of a poor design.
Is this correct?
Also, will the Weber carb bolt on directly in place of the original carb?
Thanks in advance for any advice!
Keith
-

Keith, there is nothing wrong with the Zenith-Stromberg carb if it is
running correctly. With the Weber, you would also need a new intake
manifold and exhaust manifold, so it's not a case of just swapping one
carb for the other.... Personally, I would either rebuild the Z-S carb
(you can order a kit from Moss Motors and other places) or send it out
for a rebuild. Not sure where you're located, but Joe Curto on Long
Island, NY, is a recognized carb rebuilding expert.
I have the Z-S on my '76B and have not had any issue with it that I
could not easily fix.
Also, there is an article written by John Twist of University Motors on
tuning the Z-S - Google 'zenith carb john twist' and you should be able
to find it.
Here it is -
http://www.sterlingbritishmotoringsociety.org/files/zenith%20stromberg%20tech%20tips.pdf
Good luck!
Dan D
'65 B resto project
'76 B driver
Central NJ USA

True the Zenith carbs can be tuned to give reasonable performance, but as
used one at a time on rubber-bumper Bs and other contemporary B.L. cars they
tend to be underwhelming in terms of performance. The single ZS on my ' 75
Midget was a public menace. The car wouldn't pull the skin off a rice
pudding. When I replaced it with a pair of 1 1/2" SUs on a manifold from
an earlier Spitfire the little engine just came to life.
Seems to me the stock carb on a rubber-bumper B gave a manly 65 or 66 bhp.,
hardly what one would expect from a car with sporting pretentions.
That being said, I'm not a great admirer of SUs either, having spent many
a happy hour replacing worn throttle shafts, bushing oval holes in carb
bodies, even converting the things to ball-bearing shafts. The mobile-jet
chokes are primitive to say the least. New SUs are expensive ( at least in
Canada), and quality of the examples I've seen in recent years has not been
impressive either, much like new Amals for classic bikes.
As mentioned in a prev. post, when I put the fresh engine in my ' 70 B-GT
at 100,000 miles I chucked the SUs away and replaced them with a pair of HSR
42 Mikuni flat-slides. These are simple, reliable, very well made units
usually used on bikes ( particularly hotrod Harleys). They cost me less
than a new pair of SUs, fit on the stock intake manifold quite neatly, and
outperform the SUs by a wide margin.
Stock carbs for the pre-rubber bumper Bs were 1 1/2", and the special
tuning manual called for 1 3/4" SUs for fast road work with hotter cams,
increased comp. etc. etc. At 42 mm the Mikunis are nicely inbetween those
two in choke size, and I suspect they flow better than standard SUs of
either size. They are much more compact than the stock carbs, are mounted
on rubber spiggots so are much simpler to fit or remove, and they can use a
wide array of K&N pancake or conical filters. Of course they are meant for
gravity feed in bike applications so you need to put a fuel pressure
regulator ( cheap) in the line in order to step down the pressure from the
fuel pump. Due to the slight inclination of the stock manifold I had to
adjust the float level slightly lower than stock, but once that was sorted
it was a 'set and forget' proposition.
One serious benefit is that you don't require the aid of Merlin to set or
jet the things. They respond to jetting changes and adjustments exactly as
you would expect, which cannot be said for the old SUs. Jets and parts are
much cheaper than they are for SUs or ZS units, and they are much more
easily available through better bike shops.
The only slightly awkward bit in the installation was the choke hook-up.
The carbs each have individual plunger chokes, which I linked to the choke
cable in the car by means of a dual-carb cable splitter box meant for a
Norton Domi. Those are available through classic bike shops, and are not
expensive. You need to do a bit of messing about getting the inner and
outer cable lengths right, but it is simple once you get at it.
I've messed about with SUs for the best part of 40 years, but the only
reason I'd go back to them would be if I were doing a complete concours
resto. For a daily driver or a brisk hobby car the Mikunis are light years
ahead of the game.
KH

True the Zenith carbs can be tuned to give reasonable performance, but as
used one at a time on rubber-bumper Bs and other contemporary B.L. cars they
tend to be underwhelming in terms of performance. The single ZS on my ' 75
Midget was a public menace. The car wouldn't pull the skin off a rice
pudding. When I replaced it with a pair of 1 1/2" SUs on a manifold from
an earlier Spitfire the little engine just came to life.
Seems to me the stock carb on a rubber-bumper B gave a manly 65 or 66 bhp.,
hardly what one would expect from a car with sporting pretentions.
That being said, I'm not a great admirer of SUs either, having spent many
a happy hour replacing worn throttle shafts, bushing oval holes in carb
bodies, even converting the things to ball-bearing shafts. The mobile-jet
chokes are primitive to say the least. New SUs are expensive ( at least in
Canada), and quality of the examples I've seen in recent years has not been
impressive either, much like new Amals for classic bikes.
As mentioned in a prev. post, when I put the fresh engine in my ' 70 B-GT
at 100,000 miles I chucked the SUs away and replaced them with a pair of HSR
42 Mikuni flat-slides. These are simple, reliable, very well made units
usually used on bikes ( particularly hotrod Harleys). They cost me less
than a new pair of SUs, fit on the stock intake manifold quite neatly, and
outperform the SUs by a wide margin.
Stock carbs for the pre-rubber bumper Bs were 1 1/2", and the special
tuning manual called for 1 3/4" SUs for fast road work with hotter cams,
increased comp. etc. etc. At 42 mm the Mikunis are nicely inbetween those
two in choke size, and I suspect they flow better than standard SUs of
either size. They are much more compact than the stock carbs, are mounted
on rubber spiggots so are much simpler to fit or remove, and they can use a
wide array of K&N pancake or conical filters. Of course they are meant for
gravity feed in bike applications so you need to put a fuel pressure
regulator ( cheap) in the line in order to step down the pressure from the
fuel pump. Due to the slight inclination of the stock manifold I had to
adjust the float level slightly lower than stock, but once that was sorted
it was a 'set and forget' proposition.
One serious benefit is that you don't require the aid of Merlin to set or
jet the things. They respond to jetting changes and adjustments exactly as
you would expect, which cannot be said for the old SUs. Jets and parts are
much cheaper than they are for SUs or ZS units, and they are much more
easily available through better bike shops.
The only slightly awkward bit in the installation was the choke hook-up.
The carbs each have individual plunger chokes, which I linked to the choke
cable in the car by means of a dual-carb cable splitter box meant for a
Norton Domi. Those are available through classic bike shops, and are not
expensive. You need to do a bit of messing about getting the inner and
outer cable lengths right, but it is simple once you get at it.
I've messed about with SUs for the best part of 40 years, but the only
reason I'd go back to them would be if I were doing a complete concours
resto. For a daily driver or a brisk hobby car the Mikunis are light years
ahead of the game.
KH

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